Dual battery or battery pack

To answer very short (as there is lots of posts explaining why I suggest this)Solenoid type with extra switch is the way to go. I would also suggest you use the same batteries. ie two starter batteries the same cca. Stay away from the deep cycle.

I've got a great setup. It was installed by Chris at Battery World, Wantirna, Vic. He put a smart solenoid under the bonnet, ran 140 amp cable along the chassis and popped it back into the car attached to an Anderson plug. He then put a 100 amp Lifeline "AGM" battery into a battery box. The battery box has cable running out of it to another Anderson plug so the battery can be removed when not needed or to be used as a mobile power supply. Inside the box he fitted a circuit breaker and two female waeco plugs to the box. He also added a three way cig socket plug with a male Waeco plug on the end to give me three power outlets if needed. The other female plug on the box is used to power my fridge, an Engel which I got him to fit a Waeco plug to as they clip in and stay in. Total cost $700.

AGM batteries have the advantage that they are completely sealed and will accept an extremely high recharge rate, basically whatever you can throw at them. A normal deep cycle will only take about 5 amps, so takes a lot of driving to get them back to full. AGM's of this size are reported to fully charge from near flat in 2-3 hours.

The other big advantage is the portability. Went away a few weeks ago to some unpowered cabins up the bush and was able to take the battery into the cabin to power the fridge, lights and laptop to fiddle with my photography.

I can't speak highly enough of the setup.

Keep in mind those Waeco power packs are only 48 amp.

The following is a post I made to the aus.cars.offroad newsgroup about a
year ago, it may be of interest to you:

mike_harding@fastmail.fm

A useful poor man's 2nd battery system is as follows:

Obtain a starter motor solenoid (relay) from the wreckers
yard - any 12V one will do.

Connect the solenoid (relay contacts) from the positive
terminal of your main battery to the positive terminal of
your 2nd battery. Use BIG cable, not less than 6mm CSA.
(Not sure which number cable that is in auto terms but it
should have an outside diameter of at least 5mm - ie. be
capable of carrying 30A+. Might not be a bad idea to fit
a 50A fuse too).

Connect the negative terminal of your 2nd battery to a
_really_ good earth point. (Same big cable).

Connect the solenoid negative coil terminal to earth. (Smaller
wire here, only needs to carry 3A?).

Connect the solenoid positive coil terminal to a switch. Don't
forget a fuse.

Connect the other side of the switch to an ignition dependant
positive 12V supply, ie. when the ignition if off there is
NO 12V at the switch. This ensures the solenoid will drop
out when the ignition is off in case you forget to flip the
switch. A dash mounted warning light might be useful too.

To use the above;
Ensure the solenoid switch is OFF before starting the vehicle.

Start the vehicle and allow the engine to run for (say) 30 minutes
to charge the main battery.

Close the solenoid switch, which closes the solenoid and
starts charging the 2nd battery.

When you think the 2nd battery is fully charged open the
solenoid switch.

You can buy screw type battery isolators which allow you
to disconnect the battery in a few seconds, I would strongly
recommend you fit one to each battery.

If you buy a 2nd battery of a similar size and identical terminals
to your main battery it makes a very convenient spare in the event
of a flat main.

This is a good site for all things battery:
http://www.uuhome.de/william.darden/

Mike Harding

no, you do not need a dual battery system if you are moving every day and careful with your power consumption. i didnt have one for several years with only 2 mishaps (kids/lights) but mostly i am with club members.
however, now i have duals as i travel alone sometimes and its nice to know your main batt is charged in the morning.
stay away from powerpacks and deep cycles batts.
$585 from arb sounds a lot but consider my outlay,
1) batt tray $120
2) exide extreme batt $130
3) redarc solenoid $150 ish
4) full size 'off the shelf' cables approx $75
5) sweat $lots
total around $475 for materials alone.
if you go for solenoid, try the redarc. it cant get any simpler. if the voltage drops below 12.6v it seperates the batts. the latest model has a aux wire to manually connect the batts and i have also fitted an LED in the cab.

Regardless of the type of system, I would go with dual betteries rather than the power packs, I have found them more reliable and longer lasting than battery packs, and if/when it does fail it is only $80 - $140 for a battery and not $200 - $400. Invest once and do it right. What type of vehicle do you have, others are bound to have completed this task already and cam provide detailed info.
Rolande

Depending on your own skills & confidence you can also go direct to the Rotronics web site and see what they provide if you want to fit their unit yourself. They also supply all of the do-it-yourself paperwork & wires. You will have to fit a 2nd battery tray in the eng compartment.

I"m a bit concerned about the "keep away from deep cycles" sentiment voiced above. I'm no expert on batteries but made my decision after researching it thoroughly. Apparently there are real deep cycles and some that just masquerade.

Anyway, don't take too much notice of me or anyone else who is not qualified ( and I'm not suggesting some other contributors haven't got a clue, their experiences are probably valid), but try this site.

http://www.windsun.com/BATTERIES/Battery_FAQ.htm

FASCINATING READING. That is for the poor boring sods like myself that find batteries interesting.

Good luck with your projects.

We have a dual battery setup on our Troopy. When the deep cycle battery died, we bought a normal starting battery ($40 from the markets) and have had no problems in the 18 months it has been fitted for the "house" battery

We turn the fridge (Engel) off at night . We sleep in the truck and the fridge wakes me up if left on. We use an inverter to power flourescent lights, TV, laptop, etc and never had a problem. My guess is that we could get away with a single battery.

I have not gone into the depths of how our second battery is connected as it was there when we bought the truck but it only has lite gauage cable (40amp) between the batteries and a relay seems to isolate the second battery. Simple as and seems to work. I think that the relay only operates when the ignition is on so the second battery gets charged with the engine running and is disconnected when the engine is not running.

All this has worked well for us over the last 18months but others may not be so happy with our set-up.

Be careful of cheap wet cell deep cycles , as the recharge times are longer.
Stick to a normal cranking battery, or an AGM as they will recharge at a very fast rate- which is what you want when camping.
Remember, the portable battery packs are still only a battery in a plastic box, and all have deep cycles in them, and all talk about a fast recharge - 15 amps approx.
Guess what- this is not very fast, an agm or cranker will charge a rates up to 60 or 80 amps per hour if flattened that far.
I build the outback battery chargers, and answer calls every day about these problems.